The term "Metallocene" as used herein refers to a derivative of cyclopentadienylidene which is a metal derivative containing at least one cyclopentadienyl component which is bonded to a transition metal. The transition metal is selected from Groups IVB, VB, and VIB, preferably IVB and VIB. Examples include titanium, zirconium, hafnium, chromium, vanadium, as well as rare earth metals. A number of metallocenes have been found to be useful for the polymerization of olefins. Generally, the more preferred catalysts are metallocenes of Zr, Hf, or Ti. The term "sandwich-bonded metallocene" is used herein to refer to metallocenes having at least two cyclopentadienyl groups that are both pi bonded to the same transition metal atom.
Numerous types of metallocenes are known in the art. The metallocenes of the present invention differ from most in that at least one of the cyclopentadienyl-containing radicals that is pi bonded to the transition metal has a substituent that is also bonded to a transition metal but through a carbon sigma bond to the metal. Such metallocenes are referred to herein as double bound metallocenes. Only one example of such a double bound metallocene is believed to have ever been heretofore disclosed. It is (cyclopentadienyl) ((cyclopentadienyl)(dimethyl)methane (1-indanyl)) zirconium (IV) chloride, the preparation of which is disclosed in J. Organomet. Chem., 456, 89-95(1993), an article coauthored by one of the present coinventors, see the compound of formula (4) on page 90 of that article.
Accordingly, one object of the present invention is to provide a new class of metallocenes.
Another object of the present invention is to provide methods for producing such metallocenes.
Another object of the present invention is provide a method for producing polymers by polymerizing olefins using double bound metallocenes.
Other aspects, objects, and advantages of the present invention will be apparent from the following disclosure.